Short answer: Because some bunches of extremely complicated gears are capable of self-awareness. Longer answer: We need to ask whether the reductive term "just" in your question makes the question tendentious (i.e., biased). To the question "If humans are just like the non-self-aware bunches of gears that we understand best -- such as the bunch of gears in a clock -- then how can they be self-aware?" the answer is clearly "They can't." But the latter question isn't interesting, so presumably it's not the question you intended to ask. To put it another way, humans can be bunches of gears (using "gears" only metaphorically) without being merely bunches of gears. It could well be that when a bunch of gears gets complicated enough, it becomes capable of self-awareness. Exactly how that happens is a question for neuroscience rather than for philosophy.

Good question, but I hope you didn't intend it to be merely rhetorical. Even at this early stage of our investigations, there's good evidence that the answer has to do with whether a given bunch of atoms composes a being that possesses a complex network of neurons. Some bunches of atoms, such as the bunch that composes me, do compose such a being. Other bunches, such as the bunch that composes my favorite pen, do not. Notice that we're not tempted to regard any of these similar questions as rhetorical: How can a certain bunch of atoms be more red than another bunch? How can a certain bunch of atoms have better eyesight than another bunch? And so on. I regard the question you asked as in the same boat as those.

I presume you're asking about animals on Earth. Otherwise I'd be inclined to answer "Almost certainly!" given the vastness of the universe and the mind-boggling number of planets that astronomers estimate are out there. You've asked a question that's at least partly empirical, so as a philosopher I'm not especially well-equipped to answer it. But some who are better-equipped have answered "yes": see this link .

Having read this question and Question 5466, I think I may see what you're saying. If your opponents deny that there's a dichotomy between whatever has no consciousness at all and whatever has at least some consciousness, then they're mistaken. Maybe nothing occupies the first of those categories, but it's still a genuine dichotomy. On the other hand, if they're claiming merely that consciousness comes in degrees , then their claim is compatible with the existence of the dichotomy. Compare the real numbers, which also come in degrees (of size): -1 is smaller than 0; 0 is smaller than pi; etc. Yet there's still a dichotomy between the negative and the non-negative real numbers: no real number is both; no real number is neither. Because the real numbers are densely ordered, either there's a largest negative real number or there's a smallest non-negative real number, but not both. (In fact, it's the second option: 0 is the smallest non-negative real number, and there's no largest negative real number....

You may find it interesting to read about the phenomenon of blindsight , which sounds roughly like what you're describing. My impression is that perhaps psychologists more than philosophers have investigated it, but there's at least one book on the topic written by someone trained in philosophy.